U.S. Pat. No. 4,561,982, granted Dec. 31, 1985 to Yasuhia Kurikama and Syoichiro Kajiwara discusses scale problems in cooling water systems, boiler water systems, etc. and other situations which require the use of an effective chemical for dissolving scale, or preventing its formation, or for dissolving various minerals in different environments.
The substance 1-hydroxyethane 1, 1-diphosphonic acid (commonly termed HEDPA) has been in commercial use for many years for preventing or removing mineral deposits in heat exchanging equipment such as cooling towers and boilers. HEDPA acts as a sequestrant when used in quantities below 30 parts HEDPA to one million parts water. Above 150 parts HEDPA to one million parts water it acts as a chelate. In the range 30-150 parts HEDPA for one million parts water there is a dead zone; the HEDPA does not perform. It is known that HEDPA combined with a polymeric dispersant produces a synergistic result. The polymeric not only functions as a dispersant but also improves the mineral dissolving performance of the HEDPA when the HEDPA is used in a strength above 150 ppm in water.